1. Field of the Invention
The present invention relates to a mold release agent composition. Particularly, it relates to a mold release agent composition for the molding, which is suitable for molding a shaped article made of a synthetic resin, a synthetic rubber or the like.
2. Description of Related Art
When a shaped article made of a synthetic resin such as an acrylic resin, an epoxy resin, a urethane resin, a vinyl chloride resin, a vinyl acetate resin and a shaped article made of a synthetic rubber are shaped, a mold release agent is coated on an internal surface of a mold so as to facilitate the release of the shaped article from the mold.
As the mold release agent used in such case, for example, wax mold release agents such as a paraffin wax, a wax of a higher fatty acid ester and a polyethylene wax are known. These wax mold release agents have been widely used, since they are available with the low cost and give the resultant shaped article having a good surface state.
However, the wax mold release agent has low releasing strength so that sufficient release effect cannot be achieved, unless the wax mold release agent is thickly coated on the mold when the shaped article is shaped by using a material having high adhesion strength such as an epoxy resin and a urethane resin. Accordingly, the internal surface of the mold is contaminated with repeated molding. This problem also gives an adverse effect on the dimensional accuracy of the shaped article.
The wax mold release agent disadvantageously has low adhesion strength to the mold so that the mold release agent easily migrates to the shaped article and has poor continuity of release effect. This problem results in that the mold release agent must be coated each time the shaping step is to be performed.
In addition, when the shaped article is released from the mold, a large amount of the wax mold release agent migrates to the shaped article so that the wax mold release agent gives poor fabricability (for example, printing and coating) of the shaped article surface.
As the mold release agent for solving the above problems, a fluorine-containing mold release agent a copolymer of a polyfluoroalkyl ester of (meth)acrylic acid and a substituted vinyl compound! is known (cf. Japanese Patent Kokai Publication Nos. 101319/1984 and 255404/1985).
Since the fluorine-containing mold release agent has excellent release strength, it give a sufficient release effect by thinly coating it. The fluorine-containing mold release agent has better adhesion strength to the mold than the above wax mold release agent so that it gives excellent continuity to the release effect.
However, even the fluorine-containing mold release agent cannot completely prevent the migration to the shaped article surface. The migration of the fluorine-containing mold release agent to the shaped article surface gives an adverse effect on the fabricability (printing or coating) of the shaped article surface. The reason for this is that the fluorine-containing mold release agent which migrated to the shaped article surface exhibits also the release effect against the ink and paint used for the printing and coating.
Japanese Patent Kokoku Publication No. 8425/1991 discloses a mold release agent which comprises a copolymer obtainable by polymerizing a perfluoroalkyl group-containing vinyl monomer, a phosphoric acid-containing vinyl monomer and a hydrocarbon vinyl monomer. However, since this mold release agent contains a large amount of phosphoric acid, a curing reaction was inhibited in the case of the resin and the rubber such as a urethane resin reacting during the molding step so that the appearance of the shaped article surface is not good. In addition, the reaction of the mold release agent with the shaped article results in the contamination of the mold.
From Japanese Patent Kokoku Publication No. 32514/1984, a mold release agent which comprises a mixture of a polyfluoroalkyl group-containing copolymer and a silicone resin is also known. However, since the silicone is mixed in a large amount, the shaped article surface is sticky and has poor fabricability. The silicone results in the pollution of the working atmosphere. The silicone-containing mold release agent has a problem that it gives a sticky shaped article surface and poor fabricability of the shaped article surface when it migrates to the shaped article surface.